This invention relates to valve assemblies, and more particularly, to a dynamic control valve system adapted for inflatable restraint systems for vehicles.
Currently, there is a need for improved operating characteristics for air bags as safety restraints for occupants of a vehicle for reducing the possibility of injury to such occupants during a crash. Typical air bag systems include an inflatable air bag, a source of pressurized gas, and a control mechanism. The control mechanism couples the air bag to the source of pressurized gas to rapidly inflate the air bag with the pressurized gas if the vehicle is subjected to a high rate of acceleration or deceleration, as may be caused by a crash, for example.
Most known air bag systems provide substantially instantaneous application of high pressure gas to the air bag, resulting in the air bag being inflated at a very high rate and producing large forces. Such speed and force are required in order to restrain a person of average size or larger. However, the high speed with which the air bag opens and the large force with which the expanding air bag contacts the occupant of the vehicle as the air bag is inflated may injure occupants, who are, for example, children or smaller adults. Most air bag inflation systems currently on the market are not dynamically controlled to optimally protect the particular occupant.
Many air bag systems use mechanical or pyrotechnic control inflation of systems to the air bag. This is partly attributable to the relatively slow response time of known electronically controlled valves. In some valves, mechanical springs are used to bias the valve to its closed position. The spring bias must be overcome to open the valve. The spring bias increases response time and also increases the required size of the electrical winding so that more power is required and more heat is generated. Many prior art valves are opened with pressure assist to minimize the time needed to completely open the valve. However, this pressure assist restricts the ability to rapidly close or otherwise adjust the position of the valve after opening.
In addition, known air bag inflation control systems are characterized by complex and costly structures. This is particularly true for valves that employ pressure assist or other mechanical assist. Pressure assist valves generally require a pilot valve that is operated by a differential pressures created by orificing and which initiates valve operation, by supplying operating pressure to the valve member of the main valve, or by creating a vacuum by which the main valve is caused to operate at a faster rate.
In recent years, attempts have been made to address some of these problems. One method that has been proposed by some air bag manufacturers is to use multiple inflation containers and firing only the number of containers needed for handling the crash event. However, this makes the system controls and layout more complicated. Another method that has been proposed is to use a slower inflation rate. While this can be beneficial to children and adults of smaller stature, this arrangement compromises the safety of the adults who are of average or larger size. Another method is to use multiple stage pyrotechnic devices. Most of these systems typically allow only a single change in inflation.